The present invention relates to a process of preparing N-(4-chloropyrazolyl) amidoximes which are useful as intermediates in the preparation of 1H-pyrazolo 1,5-b! 1,2,4! triazole compounds of formula (I): ##STR5##
Formula (I) includes pyrazolotriazole compounds which are 1H-pyrazolo 1,5-b! 1,2,4! triazole dye-forming couplers employed in photographic silver halide materials, wherein R and R' are independently hydrogen or a coupler substituent known in the photographic art which does not adversely affect the desired properties of the coupler. Such couplers are described in European Patent 177,765 and U.S. Pat. No. 4,540,654, for example. Additionally, formula (I) includes compounds wherein R or R' is a reactive group which can be converted to the coupler substituent, thereby providing a dye-forming 1H-pyrazolo 1,5-b! 1,2,4! triazole coupler.
The N-(4-chloropyrazolyl) amidoximes are represented by formula (II) ##STR6## wherein R and R' are independently hydrogen or a substituent as defined for formula (I).
The pyrazolotriazoles of formula (I) can be obtained from the amidoximes of formula (II) by the following cyclization reaction. ##STR7##
When amidoxime compounds which do not contain the 4-substitution on the pyrazole ring are subjected to cyclization to form the formula (I) compounds, undesirable by-products are formed. This complicates the purification of the desired formula (II) compounds and significantly lowers the yield.
Japanese kokai 63-218,665 discloses a method of making N-(4-chloropyrazolyl)amidoximes. This method involves an initial step wherein an amidoxime which contains no substitution at the 4-position of the pyrazole ring is formed, and in a subsequent step, the 4-chloro substituent is introduced to the amidoxime. However, this process has an unsatisfactory yield.
Accordingly, an object of the present invention is to provide an improved method for the production of amidoximes of formula (II). The process involves relatively simple reaction conditions and isolation procedures, and the amidoximes are produced at high yield.